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InnoDB locks and deadlocks with or without index for different isolation level

Recently, I was working on one of the issue related to locks and deadlocks with InnoDB tables and I found very interesting details about how InnoDB locks and deadlocks works with or without index for different Isolation levels. …


How to deal with MySQL deadlocks

A deadlock in MySQL happens when two or more transactions mutually hold and request for locks, creating a cycle of dependencies. In a transaction system, deadlocks are a fact of life and not completely avoidable. …


One more InnoDB gap lock to avoid

While troubleshooting deadlocks for a customer, I came around an interesting situation involving InnoDB gap locks. For a non-INSERT write operation where the WHERE clause does not match any row, I expected there should’ve been …


Percona XtraDB Cluster: Multi-node writing and Unexpected deadlocks

Percona XtraDB Cluster (PXC) and the technology it uses (Galera) is an exciting alternative to traditional MySQL replication.  For those who don’t know, it gives you: Fully Synchronous replication with a write latency increase equivalent …


InnoDB’s gap locks

One of the most important features of InnoDB is the row level locking. This feature provides better concurrency under heavy write load but needs additional precautions to avoid phantom reads and to get a consistent …


Multi-threaded replication with MySQL 5.6: Use GTIDs!

MySQL 5.6 allows you to execute replicated events in parallel as long as data is split across several databases. This feature is named “Multi-Threaded Slave” (MTS) and it is easy to enable by setting slave_parallel_workers …


On TokuMX Oplog, Tailable Cursors, and Concurrency

In a post last week, I described the difference in concurrency behavior between MongoDB’s oplog and TokuMX’s oplog. In short, here are the key differences: MongoDB protects access to the oplog with a database level …


Seconds_Behind_Master fluctuating wildly? Check for events caught in a loop

Recently I was working with a customer where we noticed that Seconds_Behind_Master fluctuating from an expected value of 0 seconds behind to a fairly high six figure value.  The servers were configured in a master-master …


Differences between READ-COMMITTED and REPEATABLE-READ transaction isolation levels

As an instructor with Percona I’m sometimes asked about the differences between the READ COMMITTED and REPEATABLE READ transaction isolation levels.  There are a few differences between READ-COMMITTED and REPEATABLE-READ, and they are all related …


Percona XtraDB Cluster reference architecture with HaProxy

This post is a step-by-step guide to set up Percona XtraDB Cluster (PXC) in a virtualized test sandbox. I used Amazon EC2 micro instances, but the content here is applicable for any kind of virtualization …